Starting device for electric motors.



No. 655,340. I Patented Aug. 7, I900.

- J. n. r. stmaas.

STARTING DEVICE FOR ELECTRIC MOTORS.

(Application filed 1000,31, 1891.

.ZwerzZar UNITED STATES PATENT .OFFIcE.

JOIIANNES IIEINRICII FRIEDRICH GORGES, OF BERLIN, GERMANY, ASSIGNOR TO THE SIEMENS & IIALSKE ELECTRICv COMPANY OF AMERICA, OF

CHICAGO, ILLINOIS.

SPECIFICATION forming part of Letters Patent No. 655,340, dated August'i', 1900.

Application filed December 31,1897. Serial rteeaoso. (No model.)

' 242,309, dated October 23, 1894; in Switzerland, No. 9,356, dated October 22, 1894; in Sweden, No. 6,308, dated October 22, 1894; in Austria, No. 45/284, dated January 22, 1895; in Hungary, No. 2,858, dated May 30,

' 18 95, and in Norway, No. 4,297, dated December 11, 1894.

' This invention relates to rotary-current and v alternating-current motors, its object being to provide means for effectively preventing 2 5 the sudden flow of excessive currents during the starting of the motor and before it has risen to normal spe'ed.

The copper coils or winding of the rotating element of an alternating-current motor of- 3o fers but very'little resistance to the passage of the current, and the electromot-ive force caused by a trifling loss in revolution below synchronous speed will be sufficient to pro- 1 duce the currents necessary for maintaining the rotation'of the movable element. In this respect the law laid down by Ferraris in his" first treatise prevails, the law being to the effect that the percentage loss of revolutions is equal to the percentage loss of work. Since 40 with magnetism remaining constant the electromotive forces in a short-circuited armature will increase in proportion to the loss of revolutions and the heat developed in the armature will increase in proportion to the square of the electromotive force, the heating eifect will also increase in proportion to the square of the loss of revolutions. \Vhen, therefore, a one-horse-power motor at full capacity with a loss of revolutions of five per cent. develops in the armature about thirty-seven'watts 5c of heat, due to the passage of the current, it will develop at the same magnetism with the armature at rest-that is, with a loss of revolutions of one hundred per cent- 37 14,800 watts,

provided the development of such a powerful current is not prevented by some means. Thus Without the provision of some starting arrangement the switching in'of the motor will practically short-circuit the armature, thereby permitting the flow of an excessivelylarge current. The powerful currents in starting will effect a very rapid starting of the motor, thereby reducing the -currents again to their normal value when the normal speed has been-attained; but in the meanwhile the winding has been subjected to a severe shock. To overcome this objection to 7 the flow of an excessive current in starting, sliding rings and brushes have been provided to conduct the developed currents to the outside of the armature,-where they are passed through a resistance adapted to be switched into circuit to maintain the currents normal until speed has been attained, when the resistance may be cut from the circuit. Another remedy consists in switching resistances or reactanees into the primary circuit, thus lessening the'tension at the terminals of the motor. The armature may also be provided with a short-circuited winding without any terminals or sliding rings.

In order to render superfluous any special apparatus, iti ias been proposed to provide two or more separate windings upon the armature, one Having a proportionally-high resistance which is always closed upon itself,- while the other,of less resistance,will be closed 9 after the motor has reached a certain speed. Another method of avoiding special starting arrangements consists in switching separate divisions of the windings of the armature into circuit, whereby the starting of the motor is efiected in a different manner from that used during constant operation. However, in applying this method it is necessary that the Y sliding rings.

currents developed in the revolving part of *the motor should always have the character of multiphase currentsthat is, the currents taken by themselves should produce a magnetic field rotating with a velocity as uniform as possible and maintaining the intensity as uniform as possible. This is the case with the usual windings of the short-circuited armatures, either where the winding is closed upon itself or where it is closed through an external resistance through the .agency of With any speed there will be -produced multiphase or rotary currents, provided there are currents in the outer ring or stationary member'of the motor capable of developing a rotating field. If the winding of the revolving part of the motor is switched in such a manner that the induced currents develop no tendency to produce a rotating field, it will be evident that at certain positions of the armature the moment of rotation will be a maximum, while in other positions it will .be but trifling. Such a motor will therefore have dead-points. lf the windings of the motor are not multiphase windings, it is possible to keep the starting-current at its proper value. It is obvious, however, that a motor having an armature with a single-phase winding will have dead-points, due to the single-phase winding, from which the armature cannot be easily started.

- The object of the present invention is to provide for such a commutation or switching of the coils of the armaturewinding as will effectivelyprevent the too sudden increase of the current when the motor is starting,

v while at the same timepreserving completely the character of the induced currents as multiphase currents. In accordance with the present invention several windings are provided on the armature and in starting these windings are switched in such a manner as '..to almost entirely neutralize their electromotive forces. When speed has been attained the windings are switched in' such a manner as to allow the development of the full electromotive forces of the windings to thereby produce the normal operating-current.

' *1 have illustrated my invention in the accompanying drawings, in which Figure 1 is a diagram of a motor embodying the principles of my invention. Fig. 2 is a'diagram illustrating a multiphase machine having two separate windings joined together so that the electromotive forces thereof will be opposed. Fig. 3 is a view showing the coils of the two windings severally joined together for the production of multiphase currents. shows a modification of the arrangement shown in Fig. 2. Fig. 5 is'a view of a modification wherein one of the windings is provided with coils divided into sections,whereby the relations between the coils of the two windings may be varied.

Like letters of reference indicate like parts in the several figures. v

Referring to Fig. 1, I have shown the fieldring I) of an induction-motor, whose coils are energized from the source of current a. The armature is supplied with two sets of windings cf 9 and e f g, suitably joined to the collector-rings o. By means of brushes the collector-rin gs are in electrical connection with terminals (1, where suitable means are provided for interchanging'the connections of the said coils. 5

In Fig. 2 the armature of the motor shown in Fig. 1 is illustrated as provided with two windings, each winding consisting, in the present instance, of three coils joinedby the star connection. One winding is provided with the three coils e f g, while the other winding has the three coils e f g. The coils of the two windings are placed in the same angular positions upon the armature and are alike, except that the coils of one winding have more turns than the coils of the other winding. The corresponding ends of the coils are placed at exactly the same point upon the armature. The ends A a of the coils e and e are connected together, likewise the eudsA (fiof the coilsfand f, and likewise the ends A a of the coils g andg. The electromotive forces of the coils e and Q will thus operate against each other, as likewise will the electromotive forces of the coils fandf and g and g. If the coils were equal, the electromotive forces would entirely neutralize each other; but due to the fact that the coils cf 9 have more turns than the coils e f g the former will develop larger electromotive forces than the latter, and in consequence currents will flow through the local circuits thus produced, due toan electromotive force equal to the difference between the electromotive forces induced in the coils e f g and those induced in the coils cf g. The local currents thus flowing will develop a rotating field, since the coils are angularly disposed in the present instance "one hundred and twentydegrees apart-thereby producing currents which are displaced in phase one hundred and twenty degrees. The rotating field thus produced starts the armature in motion.

.After the armaturehas attained the desired or normal speed the ends of the coils may be disconnected by proper switching apparatus and the ends of the coils of the two windings may be interconnected by means of the conductors h h 71 and 7c 71: as shown in Fig. 3, whereby the motor may be caused to run as a multiphase motor having two separate windings.

It is not essential that the ends of the coils c e, for instance, should be disconnected, as they may remain connected, while in addition the ends of the connected coils may be joined by the conductors h h if, as shown in Fig. 4-. Thus during the starting of the motor the coils of the several windings may be so connected that the eiectremotive forces thereof may be opposed to produce small resultant electromotive forces capable of promum currents at normal speed. .Thus the ing e" is opposed against the winding 6, and the resultant current flowing in the local circoils e f g are connected with the neutral or zero conductor D, as are also the coils e f 'g'. The opposite ends of the coils e e are joined together, as are also the opposite ends of the coilsff and g g. The coils e f g are provided with a less number of turns than the coils efg and are-furthermore divided into sections-in the present instance the sec:

tions being four in number-m m on m connected between terminals Z l Pt 1 a series of contact-brushes Z being provided adapted to be moved over the terminals and joined together by. the conductor D. In starting the brushes 1 rest upon the terminals l, in which case the whole of the windcuit, including the windings e e, is induced by an electromotive force equal to thedifiierence between the electromotive forces of the windings e and e, the induced currents beingthus a minimum. The coilsff and g g act in the same manner as the coils e c. When the brushes are moved to the terminals Z, the sections m are interconnected with the corresponding sections m, and multiphase currents thus traverse the windings in addition to the currents flowing in the local circuits. When the brushes are moved to the terminals 1, the sections m are also connected in circuit tosend multiphase currents through the interconnected windings, and as the brushes are thus advanced step by step more and more of the windings are thrown into the normal interconnected arrangement for the production of multiphase currents until the brushes rest upon the last terminals l of the series, when allof the coils are thrown into'circuit in the interconnected arrangement to produce the multiphase currents. v

There are various ways besides those illustrated of switching the electromotive forces against each other while at the same time preserying the character of the currents as multiphase currents; but those shown sufii- -ciently illustrate the nature of'the present invention and the manner of, practicing it. In the above description it has been assumed that the coils of one winding are placed exactly on top of the corresponding coils of the other winding, and'therefore the coils are precisely similar except as to their relative number of turns. a

Having thus described theinvention, what I claim as new, and desire to secure by Letters Patent, is-- 1. In an alternating-currentmotor, the'combination with a field portion, of an armatuge therefor having a multiphase winding comprising a plurality of divisions for each phase, and means for changing the connections of said divisions to vary the effective electromotive force, substantially as described.

2. In an alternating-current motor,the combination with a fie'ld portion, of an armature therefor having a multiphase winding comprising two setsof coils for each phase, and means for changing the interconnections thereof to vary the efiective electromotive force due thereto, substantially as described.

3. In an alternating-current motor, the combination with a field portion having a multiphase winding, of an armature therefor having a multiphase winding comprising a plurality of divisions for each phase and means for changing the interconnections of said divisions to vary the eifective electromotive force due to said winding, substantially as described. v i

4:. In an alternating-current motor, the combination with a field portion, of an armature therefor having a multiphase winding having a plurality of dlVl'SiOIlS for each phase, and means for connecting the said divisions in opposition to reduce the effective electromotive force and thereafter changingthe connections of said divisions to remove them 'from opposition, substantially as described.

of the other set to have the electromotive v forces due thereto opposed, thereby to decrease the eifective electromotive force, and thereafter changing the connections between said sets of coils to remove them from opposit'ion, substantially as described.

6. In an alternating-current motor,the combination with a field portion, of an armature therefor having a multiphase winding provided with two sets of coils, the coils of each set constituting in themselves a complete multiphase winding,.and means for connecting'the coils of one set with the coils of the other set to have the electromotive force due thereto opposed, thereby to decrease the effective electromotive'force, and thereafter changing the connections between said sets of coils to remove them from opposition, substantially as described. 7. In an alternating-current motor, the combination with a field portion, of'an armature therefor having a multiphaseiwindingprovided with \two sets of coils, the coils of each set constituting in themselves a complete multiphase winding, the windings of one set I being inductively associated with the windings of the other set, and means for connect ing the coils of one'set with the coils of the other set to have the electromotive force due thereto opposed, thereby to decrease the ef-v fective electromotive force, and thereafter changing the connections between said sets of coils to remove them from opposition, substantially as described.

8. In an alternating-curren t motor;the combination with a field portion, of an armature forcesdue thereto opposed, thereby to'de-- crease th e efiective electromotive force and changing the connections between said sets 'of coils to remove them from opposition, and

varying the effective number of turns of the coils of one set, substantially as described.

.10. In an alternating-current motor, the

' combination with a field portion, of an armature therefor having a multiphase winding provided with two sets of coils, the coils of each set constituting in themselves a complete multiphase winding, and means for connecting the coils of one set with the" coils of the other set to have the electromotive forces due thereto opposed, thereby to decrease the effective electromotive force and changing the connections between said sets of coils to remove them from opposition, and varying the eifective number of turns of the coils of one set, substantially as described.

11. In an alternating-current motor, the combination with a field portion, of an armature therefor, having a multiphase windingprovided with two sets of coils, the coils of each set constituting in themselves a com-- plete multiphase winding,the windings of one set being inductively associated with the windings of the other set, and means for connecting the coils of one set with the coils of the other set to have the electromotive forces due thereto opposed, thereby to decrease the effective electromotive force and changing the connections between said sets of coils to remove them from opposition, and varying the effective number of turns of the coils of one set, substantially as described.

12. In an alternating-current motor, the combination with a field portion, of an armature therefor having a plurality of coils for each phase, and means-for including the coils for each phase in opposition and varying the number of efiective turns of one of the coils for each phase whereby the effective electromotive force may be reduced and varied, sub stantially as described.

13. In an alternating-current motor, the combination with the armature thereof having multiphase-winding coils; of means for changing the interrelation of portions of the armature-winding .to create opposing electromotive forces therein, substantially as described. i

14. In an alternating-current motor, the combination with the armature thereof having multiphase-winding coils; of means for changing the.interrelation of portions of the armature -winding without destroying the multiphase relation of coils of the armature, to create opposing electromotive forces in the armature, substantially as described.

In testimony whereof I aflix my signature in the-presence of two witnesses.

JOHANNES HEINRICH FRIEDRICH GURGES. 

